The Food and Drug Administration has issued another warning to makers of dietary and workout supplements that contain the additive DMAA, or dimethylamylamine.

The warning letter, according to a report at NaturalProductsInsider.com, mirrors one the agency sent to 10 manufacturers of supplements that contain DMAA that the FDA sent to companies a few months ago. The warning told companies they must stop manufacturing and marketing these products until they submitted scientific data that not only were the supplements safe and beneficial to consumers who purchase them but also that DMAA is a natural product.

In an update to the warning letter, the FDA now cites a 1995 law governing dietary supplements because the agency is not empowered to regulate these products as they would any pharmaceutical product. In that Dietary Supplement Health and Education Act, any product containing an additive not marketed prior to 1994 must be cleared by the FDA before it is sold to the public.

The FDA says DMAA was not marketed prior to 1995 and that companies who use it in their dietary supplements must show evidence that it is safe and that it is all-natural, as manufacturers of these products claim of the additive. The agency warns makers of DMAA supplements that they must submit data showing the additive is safe and all-natural if they are to continue to be available on the market.